Image reading devices have been conventionally developed in which an image of an original is formed on a light receiving element such as a CCD (charge-coupled device) array by means of an optical system and the image data is read out. Image-reading devices may be used in devices other than facsimile and copy machines, such as projectors which display the read image data at a surface. The image data is often enlarged by being projected onto a screen. When the captured image has distortion or insufficient image resolution, these deficiencies of the image are made more apparent by projection enlargement. Therefore, a specialized imaging lens (hereinafter termed an image-capturing lens) having low distortion and high resolution is required for this kind of image-reading device.
There are also demands for compactness, high reading speed, and low price for image-reading devices. Accordingly, compactness, low price, and improved brightness are required for the image-capturing lens used with such an image-reading device.
In this circumstance, using fewer lenses allows downsizing of the image-capturing lens. However, using fewer lenses, on the other hand, requires improved manufacturing precision for the lenses, leading to difficulty in production. In particular, in order to obtain low distortion and high resolution for the projector described above, lens elements of the image-capturing lens have to be produced and assembled with high precision. Many lenses do not meet the necessary high standards for manufacture and assembly. Thus, production and assembly costs are high.
The present invention relates to an image-capturing lens that, for example, may be used to form an image on a CCD array, with the output from the CCD array being used to project a magnified image of the original. The object of the present invention is to provide an image-capturing lens having high optical performance, since the aberrations of the image-capturing lens are magnified by the projection of the image data that is read using the image-capturing lens and CCD array.